Process for preparing polymer additives and polyolefin compositions with improved paint adhesion

ABSTRACT

A process for preparing polyolefin additives containing hydroxy groups by reactive coextrusion of a polymer A containing dicarboxylic anhydride groups with at least one organic compound B having at least two hydroxy groups and a process for preparing a modified polyolefin composition containing hydroxy groups comprising the mixing of a polyolefin C with such polyolefin additives.

The present invention relates to a process for preparing polymeradditives containing hydroxy groups. It also relates to a process forpreparing a modified polyolefin compositions containing hydroxy groupswith improved paint adhesion.

The use of polyolefins, specially of polypropylene, has developed widelyin a large number of applications. In particular polypropylene basedcompositions are increasingly used for the construction of many interiorand exterior automotive parts like bumpers, lateral strips, rear viewmirrors or cowling grills. For most of these applications the automotiveparts have to be painted in order to provide them with a colour finishfor a better appearance and for their protection against negativephysical or chemical attacks.

Polyolefins in general and polypropylene in particular exhibit anon-polar nature whereas most paints are polar. Therefore the paint doesnot adhere well on the non-polar surface of parts made of polyolefins orin particular of polypropylene.

A pre-treatment of the non-polar surface is often used to improve thepaint adhesion. These treatments can involve physicochemical treatmentslike flame treatment, corona treatment, UV radiation or chemicaltreatments like etching with chlorine or the use of a primer based onchlorinated polyolefins. In Europe the polyolefin surfaces of manyautomotive parts are normally treated by a physical method, such asflame treatment, followed by the application of an adhesion primer,before the paint base is applied.

In order to reduce the cost of the above mentioned process and limitingthe negative effects on the environment caused by the use of chlorinatedpolyolefins, the automobile industry is looking for polyolefincompositions exhibiting the same good paint adhesion on their surfacebut without the need of special processing steps of physical treatmentand/or of coating the surface with a primer.

Recently polypropylene compositions have been described which have animproved paint adhesion and which consist of a mixture of polypropyleneand an additive which is a polypropylene grafted with maleic anhydride(PP-g-MA) and modified with mono- or difunctional polyethers. TheEuropean patent application EP 0 662 496 describes a method forpreparing PP-g-MA/mono- or difunctional polyether additives by mixing aPP-g-MA with difunctional polyethers in an internal mixer like a stirredvessel. This method is a time consuming procedure and most polyolefinprocessors do not have the necessary equipment like stirred vessels.

The European patent application EP188926 describes a mixture ofpolypropylene/PP-g-MA/polyols which has an improved adhesion onaluminium. It is recommended to mix all components in a singleoperation. The application of this procedure to polypropylene basedblends did not give the desired degree of paint adhesion.

Thus there is still the need to find a simple and economically optimisedmethod to produce polyolefin additives to be used as components forpolyolefin compositions with improved paint adhesion.

It is an object of the present invention to remedy the disadvantagesdescribed above and to provide an economic and efficient process forpreparing polyolefin additives containing hydroxy groups.

Another object of the present invention is to provide a process forpreparing modified polyolefin compositions containing hydroxy groupswith improved paint adhesion while maintaining their desired mechanicaland Theological properties.

Accordingly, a process for preparing polyolefin additives containinghydroxy groups characterised by reactive coextrusion of a polymer Acontaining dicarboxylic anhydride groups with at least one organiccompound B having at least two hydroxy groups has been found.

Furthermore, a process for preparing a modified polyolefin compositioncontaining hydroxy groups comprising the mixing of a polyolefin C withthe extruder product obtained by the inventive process for preparingpolyolefin additives has been found.

Polymer A can be any polymer that contains dicarboxylic anhydridegroups. The dicarboxylic anhydride groups can be introduced to polymer Aby polymerisation or copolymerisation of the appropriate monomerscontaining at least one monomer with at least one dicarboxylic anhydridegroup, or the dicarboxylic anhydride groups can be introduced by radicalgrafting of a polymer with a monomer containing a dicarboxylic anhydridegroup and a carbon-carbon double bond. Such radical grafting reactionsare e.g. described in the U.S. Pat. No. 5,451,639.

Examples of monomers containing a dicarboxylic anhydride group usefulfor polymerisation, copolymerisation or grafting are maleic anhydride,endo-bicyclo[2.2.2]oct-5-ene-2,3-dicarboxylic anhydride orcis-5-Norbornene-endo-2,3-dicarboxylic anhydride.

Preferably the process for preparing polyolefin additives containinghydroxy groups is characterised in that polymer A is a polyolefingrafted with maleic anhydride.

Examples for such polyolefins to be grafted with maleic anhydride areethylene homo- or copolymers with C₃-C₈-α-olefins, propylene homo- orcopolymers with C₂-C₈-α-olefins, 1-butylene homo- or copolymers withC₂-C₈-α-olefins, hydrogenated polybutadienes, polyisoprene, hydrogenatedpolyisoprene, ethylene-propylene-diene-rubbers and cycloolefincopolymers like norbornene-ethylene copolymers.

In particular polymer A is a propylene homo- or copolymer grafted withmaleic anhydride. These polymers are commercially available. Examples ofcommercially available grades of polypropylene grafted with maleicanhydride are Questron KA 805 from Basell, Epolene G 3003 from Eastmannor Polybond 3200 from Uniroyal.

The grafting process of polypropylene with maleic anhydride in thepresence of a radical initiator is well known in the literature and isestablished in industry. Therefore polymer A can also be produced in anextra step just before starting the inventive process.

The organic compound B which has at least 2 hydroxy groups, can e.g. bea polyol, preferably a diol. According to the present invention a partof the hydroxy groups of the organic compound B has to react with thedicarboxylic anhydride groups of polymer A under the conditions of anextrusion process. This process is called reactive coextrusion.Preferably the reactive hydroxy groups are aliphatic primary alcoholgroups represented by the fragment —CH₂—OH or secondary alcohol groupsrepresented by the fragment ═CH—OH.

None limiting examples of the organic compound B are alkanediols,alkanetriols, polyvinylalcohols, poly-(vinylalcohol-co-ethylene),polyethylene glycols or polypropylene glycols.

Preferably the process for preparing the inventive polyolefin additivesis characterised in that the organic compound B is a α,ω-alkanediol with3-12 carbon atoms. None limiting examples of such diols are1,3-propanediol, 1,4-butanediol, 1,6-hexanediol or 1,8-otanediol.

In particular the organic compound B is 1,4-butanediol.

Also preferably the organic compound B is polyethylene glycol orpoly-(vinylalcohol-co-ethylene).

Polymer A and the organic compound B are reacted together in suchamounts that the ratio of the total number of dicarboxylic anhydridegroups of polymer A and the total number of hydroxy groups of theorganic compound B are in the range of 1:0.1 to 1:20, preferably from1:0.5 to 1:10. In the case of diols is the molecular ratio of thedicarboxylic anhydride groups to the diol molecules in the range of1:0.05 to 1:10, preferably 1:0.25 to 1:6 and in particular 1:0.75 to1:4.

The reaction between the dicarboxylic anhydride groups and the hydroxygroups is done in an extruder. Polymer A and the organic compound B canbe premixed and then they can be introduced together into the entrypoint of the extruder. Another possibility is the introduction ofpolymer A at the entry point of the extruder and the addition of theorganic compound B further down the extruder. The organic compound B canbe advantageously dosed by a pump.

The temperature inside the extruder, i.e. the reaction temperature, isusually between 160° C. and 300° C., preferably between 180° C. and 270°C.

The average retention time of the reaction mixture in the extruder whichis comparable with an average reaction time is in the range of 0.5 to 5minutes, preferably between 1 and 3 minutes, most preferably between 1.5and 2.5 minutes.

The reaction of the dicarboxylic anhydride function and the hydroxyfunction can be improved by the addition of at least one suitablecatalyst such as dibutyl tin dilaurate or tetrabutyl titanate to thereaction mixture. Such catalysts are usually added in an amount of 0.001mol % to 20 mol % based on the dicarboxylic anhydride groups.

The extruder in which the process for preparing the polyolefin additivescontaining hydroxy groups is performed can be any single- or two-stagemachine. The extruder should accept solid or liquid molding compositionsand extrude the same, predominantly continuously, through an orifice.Examples of extruders to be applied in the inventive process arediskpack plasticators, pin-type extruders and planetary extruders.Machinery of this type is conventional in the plastics industry.

Preferred extruders are screw extruders, and these may be constructed assingle- or twin-screw machines.

Particular preference is given to twin-screw extruders.

According to the instant invention a process for preparing a modifiedpolyolefin composition containing hydroxy groups comprising the mixingof a polyolefin C with the extruder product obtained by the inventiveprocess for preparing polyolefin additives has been found.

The amount of the polyolefin additives in the final polyolefincomposition containing hydroxy groups is between 0.1% to 40% by weight,preferably between 1% and 25% by weight, in particular between 5% and20%.

Polyolefin C is a component essentially unreactive under the mixingconditions. The term polyolefin includes homopolymers and copolymers.Polyolefin C represents the matrix of the final polyolefin composition.

Polyolefin C can be ethylene homo- or copolymers with C₃-C₈-α-olefins,propylene homo- or copolymers with C₂-C₈-α-olefins, 1-butylene homo- orcopolymers with C₂-C₈-α-olefins, hydrogenated polybutadienes,polyisoprene, hydrogenated polyisoprene,ethylene-propylene-diene-rubbers and cycloolefin copolymers likenorbornene-ethylene copolymers.

Preferably polyolefin C is a propylene homo- or copolymer.

In particular polyolefin C is a propylene-ethylene copolymer containingup to 50% by weight of ethylene.

In particular a process for preparing a modified polyolefin compositioncontaining hydroxy groups is preferred characterised in that polyolefinC contains at least a further polyolefin additive selected from thegroup of stabilisers, processing reagents, pigments, fillers ornucleating reagents, or that at least one further polyolefin additive isadded during the process.

The particular kind and amounts of additives depend on the particularapplication of the final polymer composition and are known to a personskilled in this technical field.

Customary stabilizers are antioxidants such as sterically hinderedphenols, processing stabilizers such as phosphites or phosphonites, acidtraps such as calcium stearate, zinc stearate or dihydrotalcite,sterically hindered amines or else UV stabilizers. Generally thepropylene polymer composition of the invention includes one or more ofthe stabilizers in amounts of up to 2% by weight based on the total massof the polymer composition.

Useful processing reagents are lubricants and demolding agents such asfatty acids, calcium or zinc salts of fatty acids, fatty amides or lowmolecular weight polyolefin waxes, which are customarily used inconcentrations of up to 2% by weight.

Useful pigments or fillers for the modified polyolefin compositioninclude for example talc, chalk or glass fibers in amounts of up to 50%by weight.

Useful nucleating agents include for example inorganic additives such astalc, silica or kaolin, salts of mono- or polycarboxylic acids such assodium benzoate or aluminium tert.-butylbenzoate, dibenzylidene sorbitolor its C₁-C₈-alkyl-substituted derivatives such as methyl- ordimethyidibenzylidene sorbitol or salts of diesters of phosphoric acidsuch as sodium 2,2′-methylenebis-(4,6-di-tert.-butylphenyl)phosphate. Incase that nucleating agents are applied, the nucleating agent content ofthe propylene polymer composition is generally in the range between0.001% and 5% by weight.

Additives of these types are generally commercially available and aredescribed for example in Gächter/Müller, Plastics Additives Handbook,4^(th) Edition, Hansa Publishers, Munich, 1993.

The conditions for preparing a modified polyolefin composition by mixingat least the extruder product obtained from polymer A and at least anorganic compound B with polyolefin C are not critical. The preparationcan be done in any single or two stage machine. The used machines can beextruders like a diskpack plasticators, pin-type extruders and planetaryextruders. Other possibilities are combinations of mixers with dischargescrews and/or gear pumps.

Preferably the preparation of a modified polyolefin composition is donein an extruder under similar or the same processing conditions asdescribed above for the preparation of the polyolefin additivecontaining hydroxy groups.

The temperature inside the extruder, i.e. the processing temperature, isusually between 160° C. and 300° C., preferably between 180° C. and 270°C.

The average retention time of the mixture in the extruder is in therange of 0.1 to 5 minutes, preferably between 0.25 and 1 minute.

The preparation of the polyolefin additives containing hydroxy groups isa very time saving process because the reaction time is in the order ofa few minutes, in general less than 3 minutes. In addition this methodis a much gentler process than the long lasting process in a stirredvessel. The obtained additive of the inventive process is a veryhomogeneous product that can be directly used in the next mixing stepwith the matrix polyolefin C. In most cases this step is done also in anextruder. So a polyolefin processor can produce the polyolefin additivecontaining hydroxy groups and the final polyolefin compositioncontaining hydroxy groups in an appropriate extruder line without theneed of other special equipment like stirred vessels. The modifiedpolyolefin composition containing hydroxy groups obtained by theinventive process exhibits also better paint adhesion values comparedwith the method described in EP 188926 in which the matrix olefin C, themaleic anhydride grafted polymer A and the organic compound B are alltogether extruded in a single step.

The polyolefin composition of the present invention exhibits a betterpaint adhesion than the matrix polyolefin C alone.

The following examples are provided to Illustrate the invention,although they are not restrictive in any way.

In these examples the paint adhesion is determined using a polyurethanebase. The adhesion is tested according to the method given in the ISO2409 Standard which consists in scratching the surface and trying topull off the paint with an adhesive tape.

EXAMPLES

Paint Adhesion Test:

The paint adhesion was tested according to the ISO 2409 Standard usingthe crosshatch test and the disbondment on the grid pattern is evaluatedusing adhesive tape. The adhesion is rated in the following manner:

-   Rating 0: 0% of the varnish disbonded-   Rating 1: up to 5% of the varnish disbonded-   Rating 2: between 5 and 15% of the varnish disbonded-   Rating 3: between 15 and 35% of the varnish disbonded-   Rating 4: between 35 and 65% of the varnish disbonded-   Rating 5: more than 65% of the varnish disbonded

Example 1

Questron KA 805 A (a PP-g-MA obtained from Basell) was extruded withpolyethylene glycol (average molecular weight: 200 g/mole) at astoichiometric ratio of 1:1 (one mole of dicarboxylic anhydride to onemole of diol molecules) in a BC 21 extruder at 240° C. with a throughputof 3 kg/h. Then the resulting product was itself extruded, using thesame conditions as in the first step, with the PP copolymer Novolen PPT0016 (produced by Basell; this copolymer contains about 17% of ethyleneas comonomer). Polyolefin composition with different ratios of theextruder reaction product to the matrix polypropylene (Novolen PPT 0016)were produced (compare table 1 and 2).

The resulting products were injected to form plates for the paintadhesion tests and to form dumb-bell shaped pieces for measuring themechanical properties.

The plates were cleaned with hexane or xylene before applying the paint.The used varnish was a mixture of Macrymal SM (an hydroxylated acryliccopolymer from the Vianova Company) and Tolonate HDB 75 MX (a biurettype of polyisocyanate from the Rhodia Company). This mixture wasapplied by spray in order to obtain a more or less regular thickness of30 microns. Then the plates were placed in an oven for 30 minutes at 80°C. to dry the varnish.

The adhesion measurement was carried out on three plates, and an averagewas taken each time. TABLE 1 Mixture % PP % PP-g-MA/diol Adhesion 1(Comp. Ex.) 100 0 5 2 95 5 0 3 90 10 0.2 4 80 20 0

The melt flow indexes (MFI) and the Charpy impact resistances at 0 and−30° C., according to the ISO 179 Standard, and the modulus in tension,according to the ISO 527 Standard, were measured on the followingdifferent mixtures: TABLE 2 Mixtures Measurement Units 1 2 3 4 MFI at230° C. under g/10 min 10.7 11 12.5 13 2.16 kg Notched Charpy MJ/mm²12.9 12.9 12.1 13.3 impact at 0° C. Pre-cut Charpy MJ/mm² 8.7 7.9 7.18.0 impact at −30° C. Tensile Modulus MPa 1042 1026 1033 995

These results demonstrated that products prepared by the inventiveconcept could be painted without using an adhesion primer and/orphysical pre-treatment, while maintaining the mechanical and rheologicalproperties of the basic product.

Comparative Example 1 Mixture 4

The simultaneous coextrusion (in analogy to EP 188926) of the threestarting materials of example 1-mixture 4 (Questron KA 805 A;polyethylene glycol (average molecular weight: 200 g/mole); Novolen PPT0016 ) was carried out in a single stage. The paint adhesion test ofthis product (80% PP; 20% PP-g-MA/diol) resulted a rating of 3.

Example 2

According to example 1 Novolen PPT 0016 was extruded with the extruderreaction product of Questron KA 805 A with butane diol which wasintroduced by a pump into the extruder. The stoichiometric ratio of thePP-G-MA to the diol was changed. The paint adhesion was tested ondifferent compositions according to the above described method (table3). TABLE 3 Stoichiometric ratio of the dicarboxylic % anhydride groupsof the Mixture % PP grafted PP grafted PP/butane diol Adhesion 1 (comp.Ex.) 100 0 — 5 2 95 5 1:2 4.3 3 95 5 1:4 2 4 90 10 1:2 1 5 90 10 1:4 0.36 80 20 1:2 1 7 80 20 1:4 0.3

Example 3

According to example 2 the same operations were done except that butanediol was replaced by a polyethylene glycol of 150 g/mole (table 4).TABLE 4 Stoichiometric ratio of the dicarboxylic anhydride groups of the% grafted PP/Polyethylene Mixture % PP grafted PP glycol (150 g/mole)Adhesion 1 (comp. Ex.) 100 0 — 5 2 95 5 1:1 0.3 3 95 5 1:2 3 4 90 10 1:10.7 5 90 10 1:2 1 6 80 20 1:1 1 7 80 20 1:2 0

Example 4

According to example 2 the same operations were done except that butanediol was replaced by Desmophen 1155 from Bayer which is a polyalcoholwith ester and ether groups. TABLE 5 Stoichiometric ratio of thedicarboxylic anhydride groups of the grafted PP/ % 0.5 × Hydroxy groupsMixture % PP grafted PP of Desmophen 1155 Adhesion 1 100 0 — 5 (comp.Ex.) 2 95 5 1:1 2.3 3 95 5 1:2 2 4 90 10 1:1 1.7 5 90 10 1:2 2 6 80 201:1 0

1-10. (canceled)
 11. A process for preparing polyolefin additivescontaining hydroxy groups characterized by reactive coextrusion of apolymer A containing dicarboxylic anhydride groups with at least oneorganic compound B having at least two hydroxy groups wherein polymer Ais a propylene homo- or copolymer grafted with maleic anhydride and theorganic compound B is a α, ω-alkanediol with 3-12 carbon atoms orpolyethylene glycol.
 12. A process according to claim 11, characterizedin that the organic compound B is 1,4-butanediol.
 13. A process forpreparing a modified polyolefin composition containing hydroxy groupscomprising the mixing of a polyolefin C with the extruder productobtained by a process according to claim
 11. 14. A process according toclaim 13, characterized in that the polyolefin C contains at least afurther polyolefin additive selected from the group of stabilizers,processing reagents, pigments, fillers or nucleating reagents, or thatat least one further polyolefin additive is added during the process.